The present invention relates to a slurry conveyor system and, more particularly, to an improvement in the slurry conveyor system of the type adapted to convey the slurry by means of pressurized water.
A typical conventional slurry conveyor system of the type described has a plurality of supply pipes, a high-pressure fresh water pump connected through pipes having valves to the inlet sides of the supply pipes, a mixture convey pipe connected to the outlet sides of the supplying pipes through valves, a low-pressure mixture pump connected, through a supply passage having a valve, to the outlet sides of the inlet side valves of the supply pipes, and a low-pressure fresh water return pipe connected, through a conduit having a valve, to the inlet sides of the outlet side valves of the supply pipes.
The valve between the supply pipes and the high-pressure fresh water pump is represented by A, while the valve between the supply pipes and the low-pressure mixture pump is expressed by B. Similarly, the valve between the supply pipes and the mixture convey pipe, and the valve between the supply pipes and the low-pressure fresh water return pipe are expressed by C and D.
The mixture liquid delivered by the low-pressure mixture pump is supplied to the supply pipes, as the low-pressure mixture pump is started with the valves B and D being opened while the valves A and C are kept closed. When the supply pipes are filled with the mixture liquid, the valves B and D are closed while the valves A and C are opened, and the high-pressure fresh water pump is started. As a result, the mixture liquid filling the supply pipes are forced into the convey pipe by the pressurized fresh water.
In this known slurry conveyor, a pressure equalizing valve is disposed across each of the valve A and D. This equalizing valve is opened in advance to the opening of the valve A or D, in order to equalize the pressure across the valve A or D, i.e. to extinguish the pressure difference between the pressure inside the supply pipe and the high-pressure fresh water supply pipe or the pressure difference between the pressure inside the supply pipe and the pressure in the fresh water return pipe, thereby to facilitate the opening of the valve A or D.
Namely, if there is no pressure equalizing valve mentioned above is not used, the valve A or D, which is pressed against the associated valve seat by a large force, particularly when the valve is of the plate type, requires an impractically large opening force. In addition, the valve is worn down rapidly. It is also to be noted that, when the valve is opened abruptly, the pressurized liquid is allowed to expand rapidly with a consequent contraction of the liquid, the pressure is increased or decreased abruptly to cause a water hammer or to generate an impact and noise.
In the case where the slurry discharge pressure is not so high, only one pressure equalizing valve provided in each of the fresh water supply pipe and fresh water return pipe can function satisfactorily. However, in the event that the discharge pressure is high, e.g. 100 kg/cm.sup.2 or higher, another problem rises as to the opening of the pressure equalizing valve itself, because of too large pressure differential across the equalizing valve itself. Namely, an impractically large opening force is required for opening the equalizing valve and the wear of the equalizing valve and the valve seat is promoted. Once the valve and or the valve seat is damaged, the water under high pressure will leak through the damaged part at a high velocity to erode the valve and valve seat to shorten the life of the pressure equalizing valve.